In present day reprocessing of radioactive waste from nuclear reactors, the high-level waste is obtained in a strong nitric acid solution. The predominant radioactive substances in the waste during the first centuries are strontium-90 and cesium-137. The waste also contains, among other things, minor amounts of uranium, plutonium and transuranic elements which have considerably greater half-lives than strontium-90 and cesium-137. Those skilled in the art are generally of the opinion that it is advantageous, after a suitable period of cooling, to convert the liquid high-level waste into a solid product of good chemical resistance which is stable to leaching out of the contained radioactive substances by water and which is able to withstand heating produced by the fission products and stresses during management and transportation of the product. Materials that have been proposed for use in containing the waste include glasses such as boron silicate glass and phosphate glass, quartz, titanium dioxide, certain zeolites and other minerals existing in nature, particularly those having the ability to retain gases.
In a known method of containing high-level waste in glass, the waste is evaporated, calcined and additives are added thereto which, when heated to 1000.degree.-1200.degree. C., result in a glass melt. Calcination of high-level waste may take place at a temperature of the order of magnitude of 300.degree.-500.degree. C. and results in the waste products being transformed into oxides. The melt is poured into tight steel containers which are then transferred to a cooled and supervised storage plant.